I would go with one of the 7.3's. They had a long successful run that was only ended by the inability to make them meet the new EPA standards. I always go with the tried and true stuff as opposed to the first run of a new idea (03 was the first year for the 6.0).
I may be biased, mine is an 02 with the 7.3. The "oily dust" on the tubes is normal on mine also.